JERUSALEM - The second day of fighting between Israel and the Hamas militant group ruling the Gaza Strip left massive damage in Gaza and an increasing number of casualties on both sides on Wednesday.

High-rise buildings were flattened by the Israeli air force in Gaza while over 1,000 rockets were fired by Gazan militants toward Israel throughout the day, including a rare overnight massive barrage against the Tel Aviv metropolitan area.

This was the most intense fighting between rivalling Hamas and Israel since they fought a five-week-long war in 2014.

In what the Israel Defense Forces (IDF) dubbed Operation Guardian of the Walls, the IDF said it has killed about 30 Hamas operatives, in coordination with the Israel Security Agency.

"This was only the beginning. We will inflict blows that they have never dreamed of," said Israeli Prime Minister Benjamin Netanyahu when visiting injured civilians at a hospital in central Israel.

"We will continue our efforts to kill senior operatives," said IDF Spokesman Jonathan Conricus in a briefing jointly held by the IDF and the Israeli Foreign Ministry early Wednesday evening.